1. Field of the Invention
The present invention pertains to machines that can pump predetermined amounts of fluids at a preset pressure to a dispensing device.
2. Description of Related Art
Of particular importance in the use of catalyst activated resin or polymer systems, is the accurate metering of reactive components just prior to their end use application. Such application may occur on the outside of high-rise office buildings, in a pharmaceutical laboratory, in a boat manufacturing facility or out on a public highway or city street. In all cases, it is imperative that the device used to meter and dispense the fluids be compact, durable and highly reliable under all conditions and with all fluids.
Machines used in the prior art oftentimes use two or more independently operated pumps controlled by electronic timing devices, solenoids and switching mechanisms. Use of such multiple intervening control devices create many opportunities for misadjustment or malfunction. This, in turn, limits the machine versatility and detrimentally affects reliability.
An example of the above is described in U.S. Pat. No. 4,828,148. There, fluid is pressurized into separate opposing piston chambers. As the chambers fill, piston rods move outwardly against a cam. The cam actuates a switch which activates a motor that raises a triangular-shaped metering cam against the piston rods. As the metering cam forces the rods back into the chambers, fluid will be expelled from each chamber. The amount of material expelled is controlled by the distance of return stroke of the pistons. The stroke distance, in turn, depends on the slope of the metering cam edges.
Not only is the above system susceptible to malfunction because of its dependence on two cams and multiple control devices for operation, it also relies on an external source to pressurize the fluid into and through the system. This is cumbersome and undesirable for many uses such as in-situ applications.
An attempt to overcome the above deficiencies is shown in U.S. Pat. No. 4,228,924. There, a single driver plate is used to move three piston pumps. Each of the pump chambers are filled with a pressurized fluid component until the piston rods contact a switch. The switch actuates a powered actuator which pushes the driver plate and associated piston rods upwardly to discharge the fluid in each chamber. The fluids pass through synchronized three-way ball valves and a check valve. They are then mixed and discharged.
A significant problem with the above machine is that the piston rods are allowed to slip relative to the driver plate. This creates volumetric uncertainty in the discharge flow and potential offsets in the timing of valve movements. Such problems necessitate the use of downstream check valves to avoid pressure differentials and backflow from the mixer. Also, the pistons are clearly not designed to provide significant pumping pressure and are primarily used for metering purposes.